Dual replaceable holesaw bit

ABSTRACT

A bit for use with a drill for cutting concentric holes of different diameters. The bit includes a holder comprising first and second elongated members which are movable relative to one another from a first position to a second position and viceversa. A first separately replaceable hole saw is connected to the first member and a separately replaceable hole saw is concentrically disposed within the first hole saw and connected to the second member. The second hole saw is retracted within the first hole saw when the members are in the first position. The second hole saw extends out of the first hole saw when the members are in the second position.

United States Patent [1 1 Rivas Dec. 11, 1973 DUAL REPLACEABLE HOLESAW BIT Primary Examiner-Leonidas Vlachos [76] lnventor: Dayton F. Rivas, 62 Mt. Prospect Ammey A' Caesar et Ave., Clifton, NJ. 07013 22 Filed: Sept. 6, 1972 ABSTRACT [21] Appl. No.: 286,632 A bit for use with a drill for cutting concentric holes of different diameters. The bit includes a holder comprising first and second elongated members which are [52] Cl 408/206 955 6 43 6 movable relative to one another from a first position [51] In B25) 51/04 to a second position and vice-versa. A first separately Fie'ld 6 204 118 replaceable hole saw is connected] to the first member 36 2 6 and a separately replaceable hole saw is concentrically disposed within the first hole saw and connected to [56] References Cited the second member. The second hole saw is retracted within the first hole saw when the members are in the UNITED STATES PATENTS first position. The second hole saw extends out of the 3,672,785 6/ 1972 Byrne 408/206 first hole saw when the members are in the second po- 2,599,770 6/1952 Marcerou 408/206 X ition" 2,564,45l 8/1951 Sandberg et al. 408/206 15 Claims, 10 Drawing Figures PAIENTED 0m 1 1975 sumznrz Has DUAL REPLACEABLE HOLESAW BIT This invention relates generally to drill bits and more particularly it relates to drill bits including plural separately replaceable concentric hole saws.

It is a common practice in the construction of commercial and industrial buildings to depose electrical duct work within cast concrete floor slabs. Such ducts generally include the flat top portion disposed generally parallel to the plane of the slab. The ducts are provided to carry several electrical cables or conductors throughout the building. These cables serve to provide electrical power at various locations in the building.

In order to effectuate connections between the cables and the duct and junction boxes and the like in the building at a particular floor location, an opening is made in the concrete floor contiguous with the duct at a location at which a connection is desired. The duct itself is then drilled to render the cables therein accessible. Electrical connections to the plural cables disposed within the duct is then effected.

In the interest of speed the above described procedure has been carried out by the use of an integral drill bit including a tubular, concrete-cutting, diamond hole saw and a tubular central metal cutting hole saw disposed within the diamond hole saw and concentric therewith. In order to cut a hole in the concrete and thereby expose the duct embedded therein the central metal cutting holesaw of the bit is retracted within the diamond hole sawsThe bit is rotated by the drill to cut a hole in the concrete. When such action is completed i.e., when the metal duct embedded in the concrete is exposed, the central metal cutting hole saw is moved out of its retracted position and into the position wherein it extendsout of the end of the diamond hole saw. The bit is then rotated by the drill so that the extended central hole saw cuts a hole in the duct to expose the electrical cables therein.

Although such integral bits operate efficiently, they leave much to be desired from the standpoint of cost. Since the bit is formed as an integral unit as soon as the diamond, concrete-cutting element wears out, which occurs somewhat frequently, the bit is rendered useless and isdiscarded even though the metal cutting element may still be operative. Needless to say such action is wasteful and increases building costs.

It is a general object of this invention to provide a bit for drilling two concentric holes of differing diameters, which overcomes the aforementioned disadvantage of prior art integral,fdual-element saw bits.

It is a further object of this invention to provide a drill bit including two concentric hole saws, each of which is separately replaceable.

It is yet a further object of this invention to provide in a drill bit meansfor moving concentrically disposed, replaceable hole saws longitudinally relative to one another and for locking said saws in position, once moved.

It is still a further object of this invention to provide in a drill bit, means adapted for mounting a variety of sizes and types of separately replaceable concentric hole saws.

These and other objects of the invention are achieved by providing a dual replaceable saw element bit comprising a holder adapted to be fixedly connected to a drill, said holder including first and second elongated members which are longitudinally movable relative to one another from a first position to a second position and vice-versa, a first separately replaceable tubular hole saw connected to said first member and a second separately replaceable tubular hole saw concentrically disposed within said first saw and connected to said second member, said second saw being retracted within said first saw when said members are in said first position and said second saw extending out of said first saw when said members are in said second position.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of a drill bit in accordance with one embodiment of this invention;

FIG. 2 is a sectional view taken along the lines 2-2 of FIG. 1;"

FIG. 3 is an enlarged sectional view taken along lines 3-3 of FIG. 2;

FIG. 4 is an enlarged sectional view taken along lines 4-4 of FIG. 2;

FIG. 5 is a sectional view of the drill bit shown in FIG.

1 shown cutting a hole in a concrete building floor;

FIG. 6 is a sectional view showing the bit shown in FIG. 5 completing the hole in the concrete floor;

FIG. 7 is a sectional view of the bit shown in FIG. 5

cutting a hole in a duct disposed in the concrete floor;

FIG. 8 is a sectional viewof the concrete floor and duct therein showing holes drilled by the bit shown in FIG. 5;

FIG. 9 is a partial perspective view of a portion of a drill bit in accordance with another aspect of this invention, a portion thereof being broken away; and

FIG. 10 is a sectional view of the drill bit shown in FIG. 9 with a portion thereof being broken away.

Referring now in greater detail to the various figures of the drawings wherein like reference characters refer to like parts, a dual hole saw drill bit embodying the present invention is generally shown at 20 in FIG. 1. Bit 20 is adapted for use with a drill for cutting concentric holes of different diameters in a work piece such as for example cutting a hole through a concrete building floor slab in which a metal electrical duct is embedded to expose said duct and thereafter cutting a hole through the wall of the duct exposed thereby to expose electrical cables disposed within said ducts.

As can be seen in FIG. 1 bit 20 includes a pair of tubular hole saws 22 and 24 mounted on a holder 26, which holder is connected to a rotating shaft 28 of a power drill (not shown).

Hole saw 22 is cylindrically tubular in shape and includes two end portions, namely, upper end portion 30 and lower end portion 32. The lower end portion 32 comprises the cutting edge of saw 22. To that end a plurality of diamond cutting elements are disposed in the edge of the lower end portion 32 of saw 22.

A plurality of radial grooves 34 are spaced equidistant about the periphery of the lower end portion 32. The function of grooves 34 will be described hereinafter. The upper end portion of saw 22 is connected to holder 26 in a manner which enables the rapid connection and disconnection therefrom.

Hole saw 24, like hole saw 30 is cylindricallytubular in shape and includes an upper end portion 36 and a lower end portion 38. The outside diameter of hole saw 24 is smaller than the inside diameter of hole saw 30.

As can be seen hole saw 24 is disposed within hole saw 30 and is concentric therewith. Hole saw 24 is connected to holder 26 in a manner which effectuates the rapid connection and disconnection therefrom. The lower end 38 of saw 24 includes a cutting edge 40 made up of a plurality of cutting teeth.

Hole saw 24 is adapted for longitudinal movement relative to hole saw 22 in order to move it from a retracted position within hole saw 30 as shown in FIG. 1, to an extended position wherein its cutting edge 40 extends beyond the cutting edge 32 of hole saw 22. This latter position is shown in phantom lines in FIG. 2.

When hole saw 24 is retracted within hole saw 22 as shown in FIG. 1 hole saw 22 is adapted, when rotated by the drill (not shown) to cut a hole in a work piece. When the hole cut by saw 22 is of sufficient depth the drill bit 20 is extracted from the hole, carrying with it the plug of material cut away by the hole saw 22. The plug is removed from hole saw 22 and hole saw 24 is moved longitudinally within hole saw 22 to the phantom line position shown in FIG. 2 wherein its cutting edge 40 extends out and beyond the cutting edge 32 of hole saw 22. The drill is then moved into position such that the cutting edge 40 of hole 24 contacts the base of the hole previously cut by hole saw 22. The drill is then operated to rotate hole saw 24 to thereby cut a concentric hole of slightly smaller diameter than said first hole through the base of said first cut hole. Upon completion of such action the bit is extracted leaving a pair of concentric holes, the inner of which being of lesser diameter.

In accordance with the preferred aspect of this invention each of the hole saws is separately replaceable on the holder of the bit. For example, hole saw 24 may be disconnected from holder 26 and replaced with a similar hole saw without necessitating the replacement of hole saw 24. Conversely, hole saw 24 may be replaced with a similar hole saw without necessitating the replacement of hole saw 22. It should therefore be appreciated that the dual hole saw bit of this invention has a distinct advantage insofar as cutting costs are concerned over an integral dual hole saw bit, which bit must be replaced when either of its component hole saws needs replacement (e.g. when a component hole saw has become dull).

The means for effectuating the relative movement between the hole saws 22 and 24, i.e. the retraction and extension of hole saw 24 relative to hole saw 22 is shown in the sectional view of FIG. 2. As can be seen therein holder 26 includes two elongated tubular holding members, namely, 42 and 44. Each tubular member is cylindrical in shape. Tubular member 44 is disposed within tubular member 42, concentric therewith, and is adapted for longitudinal movement relative thereto. The outer tubular member 42 includes at its upper end 46 a plurality of internal threads 48 which engage threads 50 of rotating drill shaft 28. The outer tube member 42 includes a reduced cross-sectional portion 52 at its lower end 54 thereof. A threaded portion 56 is provided on the periphery of the reduced crosssectional portion 52. The outer holding member 42 also includes a shoulder 58 adjacent to its reduced cross-sectional portion 52.

As can be seen in FIG. 2 wall 60 of the tubular hole saw 22 includes a thickened end wall portion 62. A central hole having threads 64 therein is provided in portion 62. The threads of said hole mate with the threads of portion 56 on outer tubular member 42 when said member is screwed therein.

As should be appreciated when hole saw 22 is tightly screwed, via its threads 64, onto the threaded portion 56 of the outer tubular holder member 42 and with its end wall 62 abutting shoulder 58, the rotation of drill shaft 28 by the drill is imparted, via holder 26, to saw 22 to cause the saw to cut a hole in an abutting work piece.

Inner tubular member 44 is disposed within outer tubular member 42 and is concentric therewith. Tubular member 44 includes a lower flanged portion 66 to which the inner hole saw 24 is connected. To that end, immediately adjacent to flange 66 of inner tubular member 44 there is provided a threaded portion 68. The upper portion 36 of hole saw 24 includes an end wall 70 including a contrally threaded portion 72. Hole saw 24 is screwed onto threaded portion 68 of inner holding member 44 via its contrally threaded portion 72 until the top edge 70 thereof abuts flanged portion 66. The end wall 70 of hole saw 24 includes a pair of holes 74 which are axially aligned with respective threaded holes 76 in flange 66. A set screw 78 is provided though each of the axially aligned holes 74 and 76 and is screwed into the latter. The set screws 78 prevent the rotation of hole saw 24 relative to inner holding member 44. In FIG. 4 there is clearly shown the disposition of set screws 78 with respect to one another and to the end wall 70 of hole saw 24.

The inner tubular holding member 44 is adapted for longitudinal sliding movement relative to the concentrically disposed outer tubular member 44 to effectuate the extension and retraction of hole saw 24 within hole saw 22.

To that 'end, inner tubular holding member 44 includes an upstanding arm 80 radiating therefrom. As can be seen in FIGS. 2 and 3 arm 80 comprises a threaded screw 82 which is screwed into a threaded hole 84 in the wall of inner tubular member 44. Screw 82 includes an elongated shaft 86. A knurled nut 88 is provided on threaded shaft 86 between the head 90 of screw 82 and inner tubular member 44. The shaft 86 of screw 82 is disposed within an elongated longitudinal slot 92 cut through the wall of outer tubular holding member 42. At the upper terminal end of slot 92 there is provided an offset locking slot 96 also cut through the wall of outer tubular holding member 44. Offset slot 96 is arranged with its major axis disposed normal to the major axis of the elongated slot 92 and extending away therefrom in the opposite direction to the direction of rotation of bit 20 (for reasons to be considered later). At the lower end of slot 92 a locking offset slot 98 is also cut through the wall of outer tubular holding member 44. Like offset slot 96, offset slot 98 is arranged with its major axis disposed normal to the major axis of elongated slot 96 and extending away therefrom in the opposite direction to the direction of rotation of the bit 20.

Inner tubular holding member 44 is moved relative to outer tubular member 42 by grasping screw 82 and slid ing it along and within the elongated slot 92. As should be appreciated when screw 82 is moved within slot 92 to its lower end thereof (the condition shown in the phantom lines of FIG. 2), the inner hole saw 24 is moved to a position wherein its cutting edge 40 extends beyond the cutting edge 32 of the outer hole saw 22. When screw 82 is moved within slot 92 to the upper terminal position therein, the inner hole saw 24 is retracted completely within the outer hole saw 22.

Offset slot 96 is provided to enable inner holding member 44 to be locked in the position wherein hole saw 24 is completely retracted within hole saw 22. This position is hereinafter denoted as the upper or retracted position. Offset slot 98 is provided to enable the holding member 44 to be locked in the position wherein the tooth cutting edge 40 of hole saw 24 extends beyond the lower cutting edge 32 of the outer hole saw 22. This position is hereinafter denoted as the lower or extendedposition.

The locking of holder member 44 in the retracted or upper position is effectuated by moving screw 82 within slot 92 toward the upper offset 96 and, once upper offset 96 is reached, moving screw 82 thereinto. The knurled nut 88 on shaft 86 is then rotated to firmly contact the surface of outer tubular member 42 contiguous with the slot to lock the screw therein. The locking of holding member 44 in the lower or extended position is effectuated by moving screw 82 within elongated slot 92 toward the lower offset 98, and once the lower offset is reached, moving the screw thereinto. The knurled nut 88 on the shaft 86 is then rotated to firmly contact the surface of the outer holding member 42 contiguotts with the offset slot 98 to lock the screw therein.

In the enlarged sectional view of FIG. 3 there is shown the inner holding member 44 locked in the upper or retracted position. As can be seen therein shaft 86 of screw 82 is rotated such that it tightly abuts the surface of outer tubular holding member 42 contiguous with slot 96, thereby locking the screw therein.

As previously noted both the offset locking slots 96 and 98 extend in a direction opposite to the direction of rotation of bit 20, which direction of rotation is shownby the arrow in FIG. 3. Thisarrangement ensures that during a drilling operation, when either hole saw 22 or hole saw 24 is cutting the work piece, screw 82 will not rotate out of the locking offset slot in which it is disposed.

As can be seen in FIGS. 2, 3 and 4, inner holding member 44 includes a longitudinal hole 100 extending throughoutits length. Hole 100' communicates at its upper end with a hole (not shown)in drillbit 28. As can be seen hole 100 extends through the threaded portion 68 at the lower end of inner tubular holding member 44 and thereby communicates with the interior of both of the hole saws 22 and 24. A liquid (e.g. water) may be passed through the drill shaft 28 and hole 100 in the inner tubular member 44 to cool either hole saw as it cuts the work piece as well as carry away chips of the work piece produced by the cutting action. The Liquid is prevented from entering between the outer tubular holding member 44 and the inner tubular holding member 42 by a pair of O-rings. To that end, an O- ring is disposed within a groove in the outer periphery of inner tubular member 44 adjacent its upper end. A similar O-ring 106 is provided in a groove 108 in the inner periphery of outer tubular member 44 at its reduced cross-sectional area portion.

Operation of tool bit in cutting through a slab of concrete 110 forming the floor of a building to expose electrical conductors within a metal duct embedded therein is shown in FIGS. 5, 6, 7 and 8.

FIG. 5 shows the tool 20 in the condition wherein the inner tubular holding member 44 is in its upper or retracted position with the shank portion 86 of screw 82 disposed within locking offset slot 96. The knurled nut 88 is tightly screwed against the outer surface of tubular member 42 contiguous with slot 96. In this position hole saw 24 is retracted within hole saw 22. Hole saw 20 is brought into contact with the surface of concrete floor 112. A tubular metal duct 114 is embedded within floor 112. The duct contains a plurality of electrical conductors or cables 116. The power drill is turned on, whereupon, shaft 28 is rotated in the direction of the arrow shown in FIG. 3 to cause the outer tubular holding member 44 to which it is connected to rotate therewith. The rotation of the outer holding member 42 causes the outer diamond edged hole saw 22 to commence rotating and cutting a hole 118 in concrete floor 112. At the same time that outer hole saw 22 is rotating, inner hole saw 24 is also rotating by virtue of this connection to the rotating inner tubular holding member 44 (which is locked in position relative to outer holding member 42 by slot 96 and knurled nut 88), but is retracted. Cooling water is passed through shaft 28 and hole 100 tothe interior ,of hole saws 24 and 26. The water from the interior of hole saw 22 results in cooling the diamond studded cutting edge 32 thereof. The water also serves to flush away bits of concrete which are cut away by the rotating diamond cutting saw 22. To that end water flows through the radially arranged grooves 34 in the cutting edge 32 of hole saw 22.

When hole saw 22 has penetrated a concrete floow 112, to a sufficient depth to expose the top wall 118 of metal duct 114, i.e., when the cutting edge 32 of hole saw 22 contacts the metal top wall of the duct (such a condition being shown in FIG. 6) the drill bit 20 is retracted, thereby withdrawing hole saw 22-from the hole 120 out thereby. r i

In order to cut through the metal top wall of the duct, the inner hole saw 24 is moved to its extended position. Such action is accomplished by unscrewing knurled nut 88 from abutting contact with the surface of outer tubular holding member 42 contiguous with offset slot 96.,Screw 82 is then moved out of the upperoffset slot 96 and into the elongated longitudinal slot 92. Screw 82 is moved downward in slot 92 .until it reaches the end thereof at which time it is moved into offset locking slot 98. The knurled nut 88 is then screwed tightly into abutting contact with the surface of outer tubular holding member 42 contiguous with the offset slot 98, to lock the inner tubular member 44 in its extended position.

Bit 20, with the cutting edge 40 of the inner hole saw 24 extending beyond the cutting edge 32 of hole saw 22 is then inserted within the hole 120 and in contact with the top wall 118 of duct'1l4. The power drill is then turned on thereby rotating bit 29 to cause the cutting edge 40 of hole 24 to cut a hole 122 in the top wall 118 of the duct. FIG. 7 shows the condition wherein the inner hole saw 24 has penetrated the top wall 118 of duct 114. Once the hole has been cut, drill bit 20 is pulled back, thereby withdrawing the hole saw 24 from holes 120 and 118. During the duct drilling operation no liquid flows through hole 100. FIG.8 shows the condition of the floor and duct after the cutting operation by drill bit 20. As can be seen therein the hole 122 is concentric with hole 120 but of smaller diameter and exposes the cables 116 which are disposed within the i duct. Electrical connections can then be made to the cable within the duct.

In FIGS. 9 and 10 there is shown a portion of drill bit whose outside hole saw 22 is of the same type as its inside hole saw 24 (e.g., carbide tooth metal cutting) in lieu of the concrete cutting, diamond-tipped hole saw 22 shown in FIGS. 1 through 8.

In FIG. 9 drill bit 20 is shown with its inner hole saw 24 retracted within the outer hole saw 22.

In FIG. 10 drill bit 20 is shown with its inner hole saw 24 extending out of the outer hole saw 22.

It should be pointed out that bit 20, in accordance with this invention, is adapted for utilizing conventional, commercially available hole saws as its inner hole saw 24 and its outer hole saw 22. To that end, the diameter of the threaded portion 56 of the outer tubular holding member and the density of threads thereon is the same as the diameter and the density of threads in the central threaded end wall hole of commercially available diamond-edged hole saws (e.g. l inches long and six threads per inch). In a similar manner the diameter of threaded portion 68 of the inner tubular holding member 44 and the density of threads thereon is the same as the diameter and the density of threads in the central threaded end wall hole of commercially available carbide hole saws (e.g., of an inch long and 18 threads per inch).

It should further be pointed out that hole saws of various diameters can be utilized in bit 20 provided their threaded end wall holes are compatible with the threaded portion of the inner or outer tubular holding members to which they are to be connected and provided that the outside diameter of the inner hole saw is smaller than the inside diameter of the outer hole saw.

Unlike prior art integral dual hole saw drill bits, either of the hole saws of this invention can be replaced without necessitating the replacement of the other hole saw or of the means for moving the hole saws relative to one another and locking them in position once moved, thereby effecting savings in holeconstruction costs.

The replacement of hole saws 22 and 24 is effected by merely unscrewing the saw to be replaced from the tubular holding member to which it is connected and screwing on another hole saw onto the said holding member. For example, assuming that in the process of cutting through concrete floors the diamond cutting edge 32 of the hole saw 22 wears out, thereby necessitating its replacement by another diamond edged hole saw. To accomplish that replacement the worn out hole saw 22 is unscrewed from the threaded portion 56 of outer tubular holding member 42. The worn out hole saw is then removed from bit 20. A new diamond edged hole saw is then mounted on bit 20 by screwing the central threaded hole in its thickened end wall onto the threaded portion 56 of member 42. Drill but 20 is then ready for use.

The replacement of inner hole saw 24 is effected by unscrewing it from threaded portion 68 of inner tubular holding member 44. The old hole saw is then removed from bit 20. Once removed, a new hole saw 24 is mounted on bit 20 by screwing the central threaded portion 72 of its end wall 70 onto the threaded portion 68 of the inner tubular holding member 68. Drill bit 20 is then ready for use.

Without further elaboration, the foregoing will so fully illustrate my invention, that others may, be applying current or future knowledge, readily adapt the same for use under various conditions of service.

What is claimed as the invention is:

1. A dual replaceable saw element bit for use with a drill for cutting concentric holes of different diameters in a work piece, comprising: a holder adapted to be fixedly connected to said drill, said holder including first and second elongated members which are longitudinally movable relative to one another from a first position to a second position and vice-versa, a first separately replaceable tubular hole saw connected to said first member and a second separately replaceable tubular hole saw concentrically disposed within said first saw and connected to said second member, said second saw being retracted within said first saw when said members are in said first position and second saw extending out of said first saw when said members are in said second position.

2. The bit as specified in claim 1 wherein each of said members includes threaded portions and wherein said first saw is screwed onto the threaded portion of said first member and said second saw is screwed onto the threaded portion of said second member.

3. The bit as specified in claim 2 wherein said first and second members are tubular, with said second member disposed within said first member, said first member being fixedly connected to said drill and including a longitudinally elongated slot therein and said second member including upstanding means disposed within said elongated slot for moving said second member relative to said first member from said first position to said second position and vice-versa.

4. The bit as specified in claim 3 wherein a cooling fluid is passed through the second tubular member to effectuate cutting of said work piece.

5. The bit as specified in claim 3 wherein locking means are provided to enable said tubes to be locked in said first and said second positions.

6. The bit as specified in claim 4 wherein said second tubular member includes a plural peripheral grooves in which O-rings are disposed to seal the space between said second member and the concentrically disposed first member.

7. The bit as specified in claim 5 wherein said locking means comprise additional slots offset from and normal to said elongated slot and into which slots said upstanding means is positioned.

8. A dual replaceable saw element bit for use with a drill for cutting concentric holes of different diameters in a work piece comprising: a first replaceable tubular hole saw, a second replaceable tubular hole saw concentrically disposed within said first saw and a holder fixedly connected to said drill for mounting each of said saws on said drill and for enabling their separate removal thereform, comprising: first and second elongated members longitudinally moveable relative to one another from a first to a second position and vice-versa, said first saw being connected to said first member and said second saw being connected to said second member, said second saw being retracted within said first saw when said members are in said first position and said second saw extending out of said first saw when said members are in said second position.

9. The bit as specified in claim 8 wherein each of said members includes threaded portions and wherein said first saw is screwed onto the threaded portion of said first member and said second saw is screwed onto the threaded portion of said second member.

10. The bit as specified in claim 9 wherein said holder includes means for moving said members relative to one another between said first and said second positions and vice-versa and means for locking said members in either said first or said second position.

11. The bit as specified in claim 10 wherein said first and said second members are tubular with said second member disposed within said first member, said first member being fixedly connected to said drill and including therein an elongated longitudinal slot, said moving means including an upstanding arm connected to said second member and disposed within said alot.

12. The bit as specified in claim 11 wherein said locking means comprise additional slots offset from a normal to said elongated slot and into which said arm is positioned.

13. The bit as specified in claim 11 wherein a cooling fluid is passed through the second tubular member to effectuate cutting of said workpiece.

14. The bit as specified in claim 13 wherein said second tubular member includes plural periphal grooves in which O-rings are disposed to seal the space between said second member and the concentrically disposed first member.

15. A dual saw element bit adapted for use with a drill for cutting a hole through a concrete floor to expose a metal electrical duct therein and for cutting a smaller diameter hole through the duct once exposed, comprising a first replaceable tubular hole saw having diamond cutting edge for cutting holes in concrete, at second replaceable tubular hole saw having a metal cutting edge for cutting holes in metal and concentrically disposed within said first saw and a holder fixedly connected to said drill for mounting each of said saws on said drill and for enabling their separate removal therefrom comprising: first and second elongated members each including threaded portions thereon and being longitudinally movable relative to one another from a first to a second position and vice-versa, said holder including means for moving said members to said positions and locking means to lock said members in said positions,.said first saw being screwed onto the threaded portion of said first member and said second saw being screwed onto the threaded portion of said second member, said second saw being retracted within said saw when said members are in said first position and said second saw extending out of said first saw when said members are in said second position. 

1. A dual replaceable saw element bit for use with a drill for cutting concentric holes of different diameters in a work piece, comprising: a holder adapted to be fixedly connected to said drill, said holder including first and second elongated members which are longitudinally movable relative to one another from a first position to a second position and vice-versa, a first separately replaceable tubular hole saw connected to said first member and a second separately replaceable tubular hole saw concentrically disposed within said first saw and connected to said second member, said second saw being retracted within said first saw when said members are in said first position and second saw extending out of said first saw when said members are in said second position.
 2. The bit as specified in claim 1 wherein each of said members includes threaded portions and wherein said first saw is screwed onto the threaded portion of said first member and said second saw is screwed onto the threaded portion of said second member.
 3. The bit as specified in claim 2 wherein said first and second members are tubular, with said second member disposed within said first member, said first member being fixedly connected to said drill and including a longitudinally elongated slot therein and said second member including upstanding means disposed within said elongated slot for moving said second member relative to said first member from said first position to said second position and vice-versa.
 4. The bit as specified in claim 3 wherein a cooling fluid is passed through the second tubular member to effectuate cutting of said work piece.
 5. The bit as specified in claim 3 wherein locking means are provided to enable said tubes to be locked in said first and said second positions.
 6. The bit as specified in claim 4 wherein said second tubular member includes a plural peripheral grooves in which O-rings are disposed to seal the space between said second member and the concentrically disposed first member.
 7. The bit as specified in claim 5 wherein said locking means comprise additional slots offset from and normal to said elongated slot and into which slots said upstanding means is positioned.
 8. A dual replaceable saw element bit for use with a drill for cutting concentric holes of different diameters in a work piece comprising: a first replaceable tubular hole saw, a second replaceable tubular hole saw concentrically disposed within said first saw and a holder fixedly connected to said drill for mounting each of saiD saws on said drill and for enabling their separate removal thereform, comprising: first and second elongated members longitudinally moveable relative to one another from a first to a second position and vice-versa, said first saw being connected to said first member and said second saw being connected to said second member, said second saw being retracted within said first saw when said members are in said first position and said second saw extending out of said first saw when said members are in said second position.
 9. The bit as specified in claim 8 wherein each of said members includes threaded portions and wherein said first saw is screwed onto the threaded portion of said first member and said second saw is screwed onto the threaded portion of said second member.
 10. The bit as specified in claim 9 wherein said holder includes means for moving said members relative to one another between said first and said second positions and vice-versa and means for locking said members in either said first or said second position.
 11. The bit as specified in claim 10 wherein said first and said second members are tubular with said second member disposed within said first member, said first member being fixedly connected to said drill and including therein an elongated longitudinal slot, said moving means including an upstanding arm connected to said second member and disposed within said alot.
 12. The bit as specified in claim 11 wherein said locking means comprise additional slots offset from a normal to said elongated slot and into which said arm is positioned.
 13. The bit as specified in claim 11 wherein a cooling fluid is passed through the second tubular member to effectuate cutting of said workpiece.
 14. The bit as specified in claim 13 wherein said second tubular member includes plural periphal grooves in which O-rings are disposed to seal the space between said second member and the concentrically disposed first member.
 15. A dual saw element bit adapted for use with a drill for cutting a hole through a concrete floor to expose a metal electrical duct therein and for cutting a smaller diameter hole through the duct once exposed, comprising a first replaceable tubular hole saw having diamond cutting edge for cutting holes in concrete, a second replaceable tubular hole saw having a metal cutting edge for cutting holes in metal and concentrically disposed within said first saw and a holder fixedly connected to said drill for mounting each of said saws on said drill and for enabling their separate removal therefrom comprising: first and second elongated members each including threaded portions thereon and being longitudinally movable relative to one another from a first to a second position and vice-versa, said holder including means for moving said members to said positions and locking means to lock said members in said positions, said first saw being screwed onto the threaded portion of said first member and said second saw being screwed onto the threaded portion of said second member, said second saw being retracted within said saw when said members are in said first position and said second saw extending out of said first saw when said members are in said second position. 